This invention relates to a liner for supporting a flexible sheet material having an adhesive backing and to the composite formed by the flexible sheet material and the liner.
One finds electronic components in a wide variety of products in today's society, and these components invariably contain tiny semiconductors, which are in effect miniature electrical circuits having closely spaced conductors. These circuits are quite sensitive to electrical energy or potentials, and indeed, a discharge of only a modest potential may damage such a circuit. The same holds true with regard to induced potentials. Likewise particles of dirt can lodge between terminals or conductors and adversely affect the operation of electronic components. The continued miniaturization and increased density of circuits have rendered them and the components in which they are installed even more vulnerable to electrical discharges and foreign particles.
Static electricity represents perhaps the most troublesome source of electrical discharges--and foreign particles as well, since an electrically charged object will attract such particles. Hence, in the clean rooms where electronic components are assembled, workers wear special clothing that is free of foreign particles and grounded so that the workers and the components on which they work remain at the same electrical potential.
Many electronic components during their assembly require installation of adhesive-backed materials which are quite thin and flexible and usually take the form of labels or seals or gaskets. The typical label may identify a component or its manufacturer or it may carry a bar code. A seal, on the other hand, usually fills or closes a gap between two sections of a housing to isolate the interior of the housing and thereby prevent contaminants from entering it and adversely affecting the circuitry and other devices within it. For example, the housing for a disk drive has two clam shell sections and an adhesive-backed seal extending around it where the two sections meet. An adhesive-backed seal may also simply cover a hole in a housing. A gasket usually fits between two segments of a housing or other device, but otherwise functions much the same as a seal. Such adhesive-backed materials, when used as seals and gaskets, further shield the electronic devices in the interiors of the housing from electromagnetic radiation which is often simply referred to as "RF".
The adhesive-backed materials come adhered to liners from which they are easily peeled for application to electronic components. The typical liner essentially consists of a paper or polymer layer and a release agent on the layer. The polymer or paper layer imparts strength and a sufficient measure of flexibility to enable the liner and sheet material to separate and thus free the sheet material for application to a housing. The release agent prevents the sheet material from adhering too firmly to the liner.
Polymers--and to a lesser measure paper--have the capacity to acquire and hold electrical charges measuring into thousands of volts, and these charges are derived merely through the effects of friction or induction or both. And the polymer layers used in conventional liners see considerable friction. Much of this friction develops in the machinery where the adhesive-backed sheet material and liners are manufactured. After all, within this machinery the sheet material and liners and that from which they are assembled are unwound from coils, passed through coating equipment, slit, and subsequently rewound into coils, all of which generates friction and the electrical charges identified with friction. To be sure, the machinery at various locations contains copper brushes or other grounding devices which contact the liner and sheet material passing through it and remove much of the charge, but not all of it. Indeed, it is not uncommon to have a liners with sheet material adhered to them leave the machinery with charges exceeding 500 volts. During subsequent shipping and handling, the composite product, that is the liner with the sheet material adhered to it, experiences more friction and induction and acquires a greater charge. When the sheet material and liner are separated a further charge develops, particularly when the separation occurs in automatic applicators which apply the sheet material to electronic components. These charges, unless dissipated, will threaten any electronic component to which the sheet material is applied or is otherwise brought into contact.